【Research Highlight】Shinshu's Nozawana Pickles Boost Immune Function
Pickled Nozawana is by far the best known of the pickled vegetables hailing from Nagano Prefecture. Very little about its functionality is known, however. Associate Professor Sachi Tanaka, a member of the Institute of Agriculture, the Academic Assembly School of Science and Technology in Shinshu University discovered that polysaccharide, a type of sugar, contained in Nozawana acts on immune cells and boosts the immune system in living organisms. In this issue, we interviewed Dr. Tanaka about the association between the immune system and the diet of people in Nagano Prefecture known for longevity, a research interest that she has pursued from the perspectives of immunology and preventive medicine. - Ayu Yanagisawa
..... Excerpt from Shindai NOW (Shinshu University's public relations magazine), No. 129, published on September 30, 2021
A long, deep relationship between diet and the immune function as seen in Nozawana
The human body has an immune system that eliminates foreign invaders such as bacteria and viruses and suppresses inflammation. The immune function, however, is known to become weakened by a variety of factors, including poor eating habits, stress, and aging, and this can often lead to the development of allergy and diseases such as cancer. Diet, in particular, has a substantial impact on our immune system. Dr. Tanaka has long been studying the association between diet and the immune function from the perspectives of immunology, nutrition, and preventive medicine. Her special interest is in food culture unique to Nagano Prefecture.
“There are many mechanisms underlying the association between diet and our immune function that we do not yet understand. The functionality of pickled Nozawana, which has been a part of the diet of people in Nagano for centuries, is among them,” said Dr. Tanaka.
She started her research on Nozawana around 2015. One of Nagano Prefecture's designated “heirloom vegetables,” Nozawana is a leafy green most often used for pickling, which is grown and consumed widely across the prefecture. There are, however, not many scientific studies that have looked into its functionality. To identify what differentiates Nozawana from other vegetables, Dr. Tanaka and her team conducted screening in 49 varieties of vegetables including Nozawana. Extracts of the vegetables were administered to spleen cells of mice which regulates the immune system to study the degree of activation of the immune cells. As an indicator, they used interferon-gamma, a type of protein called cytokine produced by immune cells. Interferon-gamma is involved in proliferation and activation of a variety of immune cells in living organisms and also plays an important role in eliminating viruses and other foreign invaders. The results of the study indicated that vegetables of the Brassicaceae and Liliaceae families, especially Nozawana among others, were by far the most effective in promoting the production of interferon-gamma.
Mechanisms behind how pickled Nozawana boosts the immune system
They have also found that the production of interferon-gamma is promoted by a form of sugar found in Nozawana called polysaccharides, which are formed with multiple monosaccharides joining together. Polysaccharides stimulate a type of immune cells in living organisms called dendritic cells to produce immune cell stimulants, which act on natural killer cells, which are also a type of immune cells. This in turn promotes the production of interferon-gamma, which then further activates a variety of immune cells. That is how Nozawana boosts the immune function. In a study that compared mice that were fed with extract of Nozawana to those that were not, the production of interferon-gamma increased more in the Nozawana extract-fed mice.
Interestingly, pickled Nozawana was found to be more effective in increasing the interferon-gamma production than its raw form. “What is more, it has also been found that more 'mature' pickles that have been pickled for half a year or longer, are more effective compared to 'fresh' pickles,” Dr. Tanaka notes. And the likely factor behind it is the action by lactic acid bacteria. The more mature pickled Nozawana becomes, the further lactic acid fermentation proceeds. Dr. Tanaka looked into what types of lactic acid bacteria are active in pickled Nozawana, and exactly how they are involved in the immune function. In addition, lactic acid bacteria may also inhibit viral infections, and studies are already underway to investigate their activity on influenza viruses.
“The key to having more people understand how our diet is related to our immune system, I think, is a story. Nozawana is one of the vegetables that are close to people's heart in the Shinshu region. Every winter, you will find pickled Nozawana on the table in many families there. Nozawana has always had a story, both historically and culturally. That is its appeal,” said Dr. Tanaka.
As yet unexplored possibilities of traditional foods of Nagano as a “longevity prefecture”
In April 2021, Dr. Tanaka discovered that resistant proteins contained in kori-dofu, or frozen bean curd, also increase the production of interferon-gamma, in a study conducted in collaboration with Asahimatsu Foods Co., Ltd., a kori-dofu manufacturer based in Iida, Nagano. Kori-dofu is a tofu that has been freeze-dried to be kept as a preserved food. Over 90% of kori-dofu on the market is made by food manufacturers in Nagano Prefecture.
We asked Dr. Tanaka what she has in view as she continues her work in exploring the association between the diet in Shinshu and the immune function. “I am hoping to pursue my research in food immunology and eventually build a system that allows us to screen for immune-boosting functionality of food in a simple way. Foods that help us be healthy and keep us from getting ill – if we have a system that lets us find foods like that, it will open new possibilities for us,” said Dr. Tanaka. The diet of people in the “longevity prefecture” of Nagano may have possibilities that are yet to be explored.